Recently, the increased awareness about the negative impact of eutrophication in the quality of water bodies and the advances in environmental technology have given rise to more stringent wastewater treatment requirements and regulations. Nitrification is implemented in many urban WWTP to maintain an effluent ammonia-nitrogen concentration lower than a permit level, and often as a precursor to denitrification where there is an effluent ammonia-nitrogen concentration limit. Effluent limits are typically applied because residual ammonia may cause a critical oxygen deficit in the receiving water, potentially resulting in harm to the environment. Additionally, at high pH levels and high temperatures, the ammonium/ammonia equilibrium favors a greater free ammonia concentration, which may be toxic for aquatic and marine biota.
The subsequent increase in operational and management investments stimulates modern urban WWTPs to face the challenges of maintaining and improving effluent quality, while guaranteeing efficient and safe operations. A major requirement for achieving these goals relies on the availability of online measurements of effluent ammonia-nitrogen concentration. The online measurements of effluent ammonia-nitrogen concentration are efficient for monitoring the operation of the plants with immediate implications for environmental compliance, safety, management planning and profitability.
Moreover, the online measurement of effluent ammonia-nitrogen concentration is invaluable for an effective utilization of advanced process control and optimization strategies in urban WWTP. However, traditionally, the measurement of effluent ammonia-nitrogen concentration is performed according to a standardized method, where the protocol consists of putting the samples potentially contaminated with organic matter into specific bottles, aerating them, and adding a microbial population. This off-line laboratory measurement requires several hours. And the harsh conditions in biological treatment processes such as the activated sludge process make reliable field measurements challenging. Therefore, although the effluent ammonia-nitrogen concentration can be measured by laboratory analyses, a significant time delay in the range of minutes to hours is usually unavoidable. These results are normally too late to achieve well-timed adaptive process control accommodating influent fluctuation and other disturbances, especially for advanced wastewater treatment requiring more precise and timely controls. During the recent decades, considerable development in online instrumentation has taken place. In spite of the recent advances, such as in situ nutrient sensors and dissolved oxygen sensors, instruments still tend to get fouled. Nevertheless, trustworthy online measurement of effluent ammonia-nitrogen concentration is not there yet.
According to the above analysis, the existing detection methods of effluent ammonia-nitrogen concentration are difficult to meet the requirements of urban WWTP. Moreover, lack of suitable online sensors for monitoring the effluent ammonia-nitrogen concentration limits the effective control of effluent quality especially in urban WWTP. Therefore, a new online and accuracy detection method for the effluent ammonia-nitrogen concentration is like to be studied.
To obtain more reliable information on the effluent ammonia-nitrogen concentration in urban WWTP, we have investigated an intelligent method based on the recurrent self-organizing neural network. The objective of this patent is to develop an intelligent method for estimating the effluent ammonia-nitrogen concentration online and with high accuracy.